Gromit wrote:
...
If I understand what Lau says, a migraine shuts down part of visual cortex for a while and so creates a temporary scotoma. Is that right, Lau?
The visual effects are part of
migainous aura, which is one of the four
phases of full migraine. Nothing much about migraine is fixed. I seem to just get a couple of the visual effects.
During the "headache" stage (called the "pain" phase), there are generally no optical effects, other light sensitivity.
The Oliver Sacks book introduced me to the terms "negative" and "positive" scotoma, and he was applying them purely to the scotoma (shadow) associated with migraine aura.
The positive scotoma includes all the "shadow" effects where something is "in the way", plus IIRC those where there are distortions (long legs, twisted faces, cubist effects).
The negative scotoma is the hard one to describe. I'm not sure that it "shuts down part of visual cortex", but that's probably close to it. I'd guess it doesn't, or there would be direct evidence. I'm inclined to a view that it is a cognitive effect - in some sense I merely cease bothering to recognise anything in the affected area.
As with all the phases of migraine, the effects are temporary and have no lasting after-effects.
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